Process for recovering and utilizing values from black liquor



Oct. 24, 1933. E. G. GooDELL 1,931,536

PROCESS FOR RECOVEHING AND UTILIZING VALUES FROM BLACK LIQUOR Filed July 25. 1931 @f Z/M/d. Qaade/ YPatented oct. 24, 1933 PROCE-SSVFOR RECOVERING AND UTILIZ- rING VALUES FROM BLACK LIQUOR Edward G. Goodell,

Stevens `Point, Wis.A

Application July 25, 1931. Serial No.'5`53,041

7 Claims.

This invention relates to improvements in a process for regenerating black liquors such as are obtained in the manufacture of sulphate or soda pulp. y.

More particularly this invention relates to improvements inthe operation of smelting furnaces used in processes employed in the regeneration of spent black liquors including the recovery of their alkaline constituents and caloriflc value obtainable from lthe combustion of their organic contents. Y

In the manufacture of pulp by the soda or sulphate Aprocesses the wood is treated in closed vessels under pressure with steam and with cooking liquors. vSulphate cooking liquor is composed principally of sodiiun'hydroxide, sodium suldeand sodium carbonate, When this treatment is completed the contents of the'closed vessels are blown intov diiusers or wash'tanks where the spent cooking liquor is separated from the pulp by draining and washing. This spent liquor is known as black liquor and is generally recovered by concentration 4in vacuum-or direct heat evaporators producing a'heavy Siruplike black liquor `high in organic content and containing nearly all of the sodium compounds used in the cooking process.

The final steps in the recovery of the concentrated black liquor are 'effected by various methods. AIn som'e cases the concentrated black liquor is fed into a rotary incinerator where itis dried )and vburned to form Vwhatf is `commonly known as black ash. In other cases the heavy black liquor is sprayed directly into a smelting furnace where it is burned and the sodium compounds fused ofi and recovered. In the processes described in myvvPatents Nos. 1,779,535; 1,779,536;1`1,779,537, and 1,779,768 dated October 28th, 1930 the concentrated black liquor is rst converted into a moisture-free powder and this powder is then treated under controlled reducing conditions to reduce thesulphate to sulfide and to recover the fused sodium compounds While at the same time utilizing` the heat of combustion to dehydrate the black liquor. In all of the recovery .processes however the nal step'conpowder inV combination. This latter process-is particularly' described in my Patent No.` 1,779,537 mentioned above. y

I have now found however that in the operation of the above mentioned processes according J to my prior patents it is advantageous to control the zone Aof combustion of both the sprayed black liquor and the black liquor powder. The high temperatures obtaining in the smeltingfurnace result inthe volatilization ofthe combustible material at or very near the`point of entrance of said sprayed black liquor or powder.

If this volatilization takes place under oxidizing conditions it is accompanied almost immediately by combustion. This immediate combustion is'70 not conductive to best results, as it reduces the overall efliciency of the reduction ci the sulphate to sulfide; I 'l f lI have found that it isvpossible to control the combustion by introducing an inert gas into the l smelting furnace at or near the point fof `entrance of the sprayed black liquor or dried 'black'liquor powder. This inert gas has the effect of retardingthe combustion ofthe volatile constituents and permits the sprayed concentrated liquor or the dried black liquor powder to be projected into the smelting furnace for some distance before combustion of its organic content occurs.

. A preferred embodiment of` my novel control feature resides in the supplying of a heated inert gas which, inthe case of spraying the black liquor directly into the smeltingV furnace'A has the additional advantage of acting asa `drying and evaporating agent to expel moisture from the sprayedblack liquor priorto combustion of its organic content. Y f 1 It is therefore an objectof this invention to provide a process for controlling the combustion of black liquor inasmeIting furnace. f f

It is a further object of this invention to provide a process for controlling the smelting furnace operation Vin the regeneration of black liquor, whereby the combustion of the lorganic `constituents in the' blackliquor is retarded to produce a :more eicient and economical-operation. M

A specific object-of this invention is to provide an improved process of regenerating black liquor to recover valuable alkaline substances therefrom by introducing the black liquor into a 105 'smelting furnace in the presenceI of an inert gas.

Other and further-important objects of this invention will be apparent fromthe disclosures in the specification and the accompanying drawing. l A Y 110 lspeed controls.

This invention l(in a preferred form) is illustrated in the drawing and hereinafter more fully described.

In the accompanying drawing Ywhich illustrates more or less diagrammatically the means for carrying out my invention, the reference numeral 1v indicates a spray drier into which concentrated black liquor is ied fromv spray devices 2.v Evaporation in the 'spray drier 1 is effected by hot flue gases. The dried black liquor collects in the bottom of the spray drier 1 is removed therefrom by a spiral conveyorBO or by other means and is blown together with of a blower 4 suitably drivenbyY any `power means such as a motor 5. The'dried blackl liquor and flue gases romtheduct :Sfare led into a cyclone powder collector 6, whereinthel Ydried black liquor powder may be freed from the iflue gases. The cyclone powder. collectedl may if desiredbe operatedso'that:apartof the flue gases remain admixed with the idried black liquor by.closingtheV .damper -7 in the gas outlet matter in xthe dried; black liquorfed to Lthe :meltrlgzllrneo iS Vpartially burned and the hot EaiiQSfiOf :ihS lvaltinlzcombustion are directed into a steam boiler or generator 13 whereadditional air is introduced throughope-nings aor` nozzles 2.3 in vthe boiler :setting and .oom-plete combustion of the gases- :takes .place Part ,1 of atheoaloric `:value of y.these gases is expended in supplying .steam which mayrrbe Vused to. rung-the evaporators tov concentrate .the `:weak l black liquor sntlioiently thatit may be fed into the spray drier and into the smeltingffurnace as `shown. The flue gasesVafter'passing through the boiler 113 stillcontain a Vvalualzele heat contentwhich heretofore was allowed-to go either up the stack 14v or, .in .accordance with -my previous-inventions;'tocthe spray drierll. According to ,my present invention, however, part of the fluezga'ses uponleaving :the steam boiler aredrawnthrough a duct l'bymeans'of a fan 16 and Iblown into the 4srnelting furn'a'c'e 10, as at 27. Another part of the flue gases is allowed topassthrough the "spray drier 1where -theircaloric content is utilized in dehydrating the concentrated black Vlliquor. A damper larrrangernent"is provided at l1'? to automatically release-the iluegases-to the stack 14 when vthe flue to drier 1 isfclosed and Vice versafto automatically closethe passage to the stackV 14 whenY drier l is-in operation. A further l'damper arrangement `18 -may be provided vin the duct 15 to regulate the vamount of gases passing through the duct butordinarily this is not necessary since this', mayI loefregulated `by the f an -16 which is preferably :provided with' variable 'In theprocess where the smelting furnace is fed both with dried black liquor and with ,con-

centrated black liquor, ja spray device'19 `is los cated near the top of the smelting Vfurnace 10 1n the path of the incoming ilue gases from the ian 16 throughthe pipe line or duct 20. The incoming hot flue gases envelop the spray from Y19 and cause a partial dehydration of the conv.bythe flue gases from the fan 16 as well as from the ue gases from the cyclone separator with,wlliclfiitV 'mayfjbe admixed. the flue gases through a duct or pipe `3 by meansl.rv

p -Whenthe driedeblack liquor from the feed 9 as well as the partially dehydrated black liquor `from the spray A19 reach the lower party of the *f srnelting furnace lo the organic material is burned Aoff and the gaseous products of combustion pass into the steam boiler 13 and from thence partly throughrtheyduct l5 and partly through'the sprayldrier 1. e *t .Inordinary practicetherueeases of the steam boiler are discharged at temperaturesof around :500 to-;600." F. .Heretofore `part of these ilue gases were' allowed tobe drawn up the stack 14 and `,their heat value was vtlfierefore wasted. By `means of my improved process it is v.possible to completelyrshut olf Y ,the stack le from the operation'by closing the damper A 17 to the stack and using practicalllell of the calorii-"ic value of thc nue-gases kfrom fthesteam boiler in the process of recovering the black liquor. The relatively cool gases .ma'ythen finally be discharged from the process through theV exitA 8of the cyclone collector 1 and thence through scrubber (not shown) Y Y If'desired, flue gases may betaken'by fan 116 from the boiler at a point where-.the temperature of these gases reaches -1-,000 or even higher sov that the difference in temperature may be expended in the ,evaporationfof the `concentrated black liquor-.rather than in the forma-V tion of steamingthe'boilers.` Y Y `The cyclone separator :isordinarily operated underlback pressuren order to ,furnish a current of flue gases tothe ,feedconveyora In llo this operation the inert flue eosesrhavenoavailable calorific content but merely serve vtoxassist inregulating the delivery of :the dried black liquor powder to Athe furnace and in `retardinsr sulphate lost in the process.

y Under they conditions `Vobtaining'in the smelting furnace, the ksodiunri compounds lare fused and are allowed tovflowffrom the smelting furnaoe,;as at .2 1, into adissolving-tank 22 wherein they are dissolvedin water and reused in the pulp cook-ing operation.

, fItwill thus be seen fromg-the above discussion .or myV-invention that the essential characteris- .tics of lmyiirnproved process Yreside vin therpro- -vision of .a pre-.dehydrationgof the-concentrated black liquor inl-the smelting-'furnace prior to its combustion together with a retardingof comist bustion. This method of operation has been.

,foundtolbe of much practical value in the operation of smelting furnaces of the type described and :forms an important developmentin .the-processof regenerating black liquor.

'Ihe retarding of combustion of Vthe organic materials present in the black liquor permits the substantially dehydrated black liquor to be deposited near the bottom of the smelting furnace before material combustion occurs. This causes a building up of a bed of burning dried black liquor and fused metallic values which flow from the bottom of the smelting furnace in a molten state. Being out of the turbulent area of the smelting furnace created by the flaming gases higher up in the furnace the alkali metal values are smoothly fused off without being volatilized. This causes an increased efficiency in the recovery of the alkalis since their volatilization is reduced to a minimum.

The building up of a bed of fused and burning materials near the bottom of the smelting furnace also increases the reduction of sulphate bodies to sulfide bodies in theevent of regenerating black liquor from sulphate pulp.

I am aware that many changes may be made and numerous details of construction may be varied through a wide range without departing from the principles of this invention, and I therefore do not purpose limiting the patent grantedhereon otherwise than necessitated by the prior art.

I claim as my invention:

1. The process of recovering the alkaline values and utilizing the heat Value of black liquor which comprises partially* burning black liquor solids in a relatively deep bed in a smelting furnace, supplying a limited amount of air to said bed tok maintain reducing conditions therein, fusing off the alkaline values therefrom, supplying additional air to the rising burning gases from the bed to thoroughly burn the same, directly utilizing heat from the burning gases in a steam generator to produce steam, subsequently passing the hot and now inert gases into direct contact with black liquor in nely comminuted form to dehydrate the same and introducing the dried black liquor powder so formed together with some of the inert gases into the smelting furnace to allow the powder to drop onto the fuel bed before being substantially burned.

2. The process of claim 1 in which part. of the inert gases from the steam generator zone are admixed With sprayed black liquor in the smelting furnace to evaporate the said black liquor and allow the residues obtained to be projected toward-the fuelk bed of the furnace before being substantially burned.

3. In the process of recovering alkaline values and utilizing the heat values of black liquors, the steps which comprise feeding into a furnace a concentrated black liquor in the presence of an inert gas and dried black liquor solids admixed with an inert gas so as to retard combustion of the organic and carbonaceous materials in the black liquor and allow the same to be projected into the furnace toward the fuel bed without substantial burning, burning the black liquor solids in the fuel bed under reducing conditions and draining off thel molten alkaline Values from the fuel bed.

4. In the process of regenerating black liquor the steps which comprise introducing dried black liquor solids into a smelting furnace in admixture with an inert gas to prevent combustion of the black liquor solids near their point of entrance into the furnace, partially burning the black liquor solids in a fuel bed located near the bottom of the furnace, supplying additional air to the rising burning gases from the fuel bed at a point in the furnace above the place where the black liquor solids are introduced to thoroughly burn the gases and utilizing the heat of combustion for the generation of steam and dehydration of further quantities of black liquor. 5. In the process of recovering alkali metal values and heat resulting yfrom combustion of black liquor, the steps which comprise introducing into a smelting furnace concentrated black liquor and black liquor powder together with inert gases to retard combustion of the organic materials present in the black'liquor.

6. In the `process of regenerating black liquor the steps which comprise spraying concentrated black liquor into contact with hot inert gases into a smelting furnace, feeding dried black lquor solids admixed with inert gases at a point in the furnace below the spray, allowing the residual black'liquor solids to be deposited on the fuel bed of the furnace, partially burning the black liquor solids in the fuel bed and recovering the alkali metal Values therefrom.

7. In the process of recovering alkali metal values from black liquor in a furnace and utilizing part of the heat resulting from combustion of the black liquor to produce steam in a steam generator, the step which comprises introducingl black liquor into the smelting furnace in finely comminuted form admiXed with hot inert gases from the steam generator region, said liquor and gases being projected downwardly into the furnace to envelop the comminuted black liquor thereby evaporating the same and allowing the resulting residues to be projected toward the bed of the furnace before being substantially burned.

' EDWARD G. GOODELL. 

